1. Field of the Invention
This invention relates to what is referred to in the art as vacuum blasting, and more particularly, to a sealed waste transfer system for vacuum blasting machines using recyclable abrasives.
As will be appreciated by those skilled in the art, vacuum blasting refers to an improved technology for cleaning and preparing surfaces by blasting the surface with an abrasive entrained in a relatively high velocity air stream. In vacuum blasting, a small hood surrounds the blasting nozzle and a vacuum port within the hood, adjacent the nozzle, sucks up the abrasive and debris particles loosened from the surface being blasted. This abrasive and debris mixture passes through a hose to a separator, where the debris (i.e., dust) particles are separated from the abrasive. The separated debris particles are deposited in a closed waste chamber, which is maintained below atmospheric pressure during the blasting operation. Abrasive separated from the debris is returned to a hopper and used again in the blasting operation. This invention supports vacuum blasting machines which recycle abrasives such as steel grit, aluminum oxide and walnut shells. Vacuum blasting machines of the type thus far described are commercially available from applicants' assignee and an example is shown schematically in FIG. 1.
It will be appreciated that vacuum blasting machines provide closed-system blasting by making the blast head in effect a small "containment structure." The coating and/or corrosion materials removed from the surface being treated, plus spent abrasive, are all deposited into a closed waste chamber. In operation, the system is virtually dust free and, therefore, relatively safe for the operator and the environment, even when blasting surfaces covered with potentially hazardous materials, such as lead and radioactive contaminants. While generally satisfactory in operation, applicants have identified a potential weak point where some debris in vacuum blasting systems can escape.
Periodically, the waste chamber of the vacuum blasting system is emptied into a removable container, such as a waste collection drum. To this end, the waste chamber is provided with a waste dump, which comprises a housing extending from the waste chamber and a bellows valve within the housing. Inflated, the bellows valve seals the waste chamber and deflated allows dust from the chamber to flow through the dump into the drum. In the prior art, an opening in a removable container (i.e., a drum) is placed beneath the dump housing. Typically, the waste chamber is externally or internally vibrated in order to facilitate the flow of dust into the removable collection drum via the dump housing. Dust may escape during this transfer operation because there is no prior art containment structure at the interface between the waste chamber dump and the waste collection drum. Moreover, even if a containment structure were erected around this interface, dust left on the walls of such a containment structure would be a potential hazard.